Neurologically, one of two networks dominate the activities of the brain: a default mode (medial and pre-frontal), which operates during waking life and does not focus on a known task, but is characterized as mind-wandering; and a cognitive control network (temporal), which operates during conscious execution of a specific task. It is in the default mode that language reflecting a person's unguarded language facility unconsciously is expressed.
Prior research suggests that schizophrenia and clinical depression co-occur when a decrease in regulation of the default mode network by the cognitive control network occurs. Researchers further suggest that cognitive deficits that may provide early warning mechanisms for mental illness, for example, such as dementia or Alzheimer's disease (AD), may be detected by analyzing changes reflected by a person's use of language over time. However, a person affected by certain mental illnesses may be able to conceal, at least early stage, cognitive deficits by applying conscious strategies and tools. This attempt to hide the deficits can therefore hinder early detection of such mental illnesses.
Detection, and in particular early detection, of mental illness can be a critical tool. As an example, forms of dementia, including AD, are among the most prevalent geriatric conditions affecting a large proportion of the aging population. Clinical assessment of dementia, involving several diagnostic procedures, may be highly stressful for the individuals undergoing diagnosis. So far, a definitive diagnosis can be made only post mortem. But while there is no proven cure for many types of dementia, a correct, timely diagnosis is of great importance. A sufficiently early diagnosis of mental illness, such as dementia and AD, may even make prevention possible.
Some mental illnesses are believed to begin years before symptoms appear. For example, some researchers, have found that Alzheimer's pathology likely begins many years before the onset of symptoms and that it may even begin decades before onset.
Such researchers suggest that diagnosis of the disease through the use of biomarkers before symptom onset may be a means of prevention (Blazer and Steffens 2009).
Recent studies further suggest that early diagnosis of some mental illnesses can also be achieved through linguistic analysis. The fact that the disease negatively affects the linguistic abilities of patients in both speech and writing presents the possibility of developing non-intrusive evaluation techniques that require minimal involvement from the patients, by looking for diachronic changes in their writing. If a person's corpus of writing is available, for example, such as in an online format (which may include a lifetime corpus of writing), researchers posit that this could be used in conjunction with clinical assessments or on their own as an early detection tool.
Prior art methods of linguistic early detection of dementia generally summarize lexical and syntactic changes in healthy aging and in dementia; a more-detailed discussion is given by Le (2010). Kemper et al. (2001) and Burke and Shafto (2008) report that in healthy aging, vocabulary increases through the middle adult years, but then may start to decline. In dementia, vocabulary declines much more rapidly, especially the use of low-frequency and more-specific words (Bird et al. 2000, Maxim and Bryan 1994, Burke and Shafto 2008), a consequence of which is that the patient's noun-to-verb ratio changes as more low-image verbs are used (Bird et al. 2000). Moreover, lexical repetitions increase (Nicholas et al. 1985; Smith et al. 1989; Holm et al. 1994, Cook et al. 2009); ideas from previous utterances are often reiterated in the same words, phrases, or even short sentences, either as perseverations or as markers when other lexical items are not available (Maxim and Bryan 1994: 183); fillers (“um”, “ah”) and dysfluencies increase (Burke and Shafto 2008).
The syntactic complexity of language, defined by measures such as clauses per utterance, declines with age in both spoken and written language (Burke and Shafto 2008). Maxim and Bryan (1994) report that left-branching clauses in English are more difficult for elderly adults to process than for a younger control group. Kemper et al. (2001), in a longitudinal study following linguistic changes in healthy elders and dementia patients, found decline in grammatical complexity to be far more rapid in the latter. Bates et al. (1995) found that use of the passive voice, in particular, was affected, with healthy elders producing fewer than a younger control group, and Alzheimer's patients far fewer again. Moreover, the AD group used more agentless passives (e.g., “John was fired” or “John got fired”) than either of the control groups, and also relied heavily on the get form of passive.
Researchers creating prior art diagnosis methods generally agree that any decline that may occur in normal aging is accelerated in the presence of mental illness, for example, such as dementia and AD. The distinguishing feature between a disease-related linguistic deficit and the natural decline associated with advancing age, then, is the rate of change, which is more gradual and less severe in healthily aging adults. In the case of mental illness, and dementia in particular, deficits in lexical features may be more prominent than in syntactic ones, since a core of linguistic ability is possibly spared until the later stages of the disease progression. The prior art does not offer an accurate system or method of diagnosis of mental illness utilizing linguistic markers.